This investigation is concerned with the isolation, purification and characterization of multiple forms (isozymes) of phenylalanine-pyruvate transaminase (PPT) (EC 2.6.1. Aminotransferase, the exact EC number has not been assigned), which is involved in phenylalanine metabolism. The purification of each form of the enzyme will be accomplished by column chromatography (DEAE-Cellulose, Sephadex, electrophoresis) and affinity chromatography. Specific antibody will be prepared to the chromatographically pure and homogeneous forms of PPT. Substrates specificity, inhibitor sensitivity and immunochemical properties of each form of this enzyme will be studied. The mechanism of enzyme induction caused by glucagon and cyclic adenosine 3',5'-monophosphate (cAMP) will be studied by pulse-labeling the enzyme with precursor amino acid. The ratio and biochemical properties of multiple forms of PPT in Hepatoma H-35 cells, normal liver cells, rat carcinosarcoma 256, murine B16 melanoma, and tumor-bearing animals will be investigated and compared with that of the normal liver. Antitumor agents, such as mimosine, etc. will be studied as inhibitors of the multiple forms of the enzyme. Attempts will be made to ascertain whether there is any correlation between enzyme inhibitory effects and antitumor activity. Once the structural requirement of the specific inhibitor is established, analogues of the inhibitor will be designed, synthesized, and tested on the purified enzyme.